Misconduct can be serious. After investigation, dismissal can be appropriate. A person can be suspended with pay.

Gross misconduct is misconduct so serious and obvious as to justify instant dismissal - 'Clear off -now'. Suspension without pay pending investigation.

Since the striker has already absented himself without oay, the distinction in this context is purely academic. There is usually little purpose in an employer describing something as gross misconduct. He can achieve the same result much more safely at the cost of a couple of weeks' pay.